SOLID BOWEL SCREW CENTRIFUGE

Description

[0001] The invention relates to a solid-wall screw centrifuge according to the preamble of claim 1 and to a method for operating such a solid-wall screw centrifuge according to claim 3.

[0002] Solid-bowl screw centrifuges are used to separate or clarify a suspension into at least one liquid phase and one solid phase. In such solid-bowl screw centrifuges, radial shaft seals are often used to protect one or more bearings, especially rolling bearings, from suspension ingress. For example, a sealing cage of the radial shaft seal is inserted into a bearing housing, while a sealing lip rests on a rotating shaft. Due to the high circumferential speeds of the shafts in the solid-bowl screw centrifuge, the sealing lip of a radial shaft seal is subject to considerable wear.

[0003] To ensure a sufficient sealing function of a radial shaft seal, the sealing lip is pressed against the running surface or mating surface of the rotating shaft. The contact force can be generated by the elastic sealing lip, which, in its uninstalled state, has a smaller diameter than the diameter of the shaft forming the mating surface. During installation of such a radial shaft seal, the elastic sealing lip is stretched to the diameter of the shaft, with the restoring force of the elastic sealing lip generating the desired contact force or surface pressure of the sealing lip. The contact force can also be further increased by a ring spring or serpentine spring.

[0004] The higher the contact force of the sealing lip, the higher the frictional power of the sealing lip and thus the heat input into the shaft bearing. The resulting increase in bearing temperature is undesirable. The main influencing factors for friction losses are the design of the radial shaft seal used, the material of the sealing lip, the contact force with which the sealing lip is pressed against the shaft, the rotational speed of the shaft, the precision with which the shaft was manufactured, the surface finish of the shaft or the mating sealing surface, and the type of lubrication of the bearing points to be sealed.

[0005] According to literature, the friction losses of a radial shaft seal with a diameter of 110 mm and a shaft speed of 6500 rpm can amount to approximately 700 W and are therefore not insignificant.

[0006] Additionally, the wear of a radial shaft seal in a solid-jacket screw centrifuge is increased if a suspension to be clarified comes into contact with the radial shaft seals, especially if it is an abrasive suspension, such as sewage sludge.

[0007] Only when the bearing is damaged due to leakage does this lead to detectable vibrations, noise, or a significant temperature increase. These indirect consequences of seal leakage can be monitored. The current degree of wear, and thus the likely point of failure of a radial shaft seal in a solid-bowl screw centrifuge, cannot be automatically detected, estimated, or predicted for predictive maintenance purposes.

[0008] From DE 34 30 508 A1, a filter centrifuge for separating solid and liquid components in a suspension is known, comprising a rotating drum with filtrate passages. The centrifuge drum is mounted on a machine frame via a shaft supporting the drum, using rolling bearings. The rolling bearings are sealed by at least one seal located between the shaft and the machine frame to prevent the ingress of suspension components. The protective effect of the seal is particularly high because the seal comprises two radial shaft seals arranged axially apart on the shaft, forming a gap. This gap is vented to the atmosphere via a vent channel. A disadvantage of this solution is, among other things, the inability to estimate or predict the total failure of a radial shaft seal.

[0009] As an example of the state of the art, US 2016 0310 969 A1 can be cited, in which a bearing of a decanter is cooled, which is arranged between two radial shaft seals. A chamber between these seals is cooled with fluid that is fed into the chamber and then discharged from it.

[0010] DE 2 212 165 A discloses a sealing arrangement for a shaft in which two radial shaft seals are arranged in opposite directions. These seals thus define a chamber. Air, for example, is introduced into the chamber through a bore and a throttle. The gas pressure in the chamber is adjusted so that gas escapes from under the sealing lips of the radial shaft seals.

[0011] The state of the art is further evidenced by the generic CN 112 228 565 A.

[0012] Against this background, the invention aims to minimize wear on radial shaft seals in a simple manner. Furthermore, a further development is intended to improve the predictability of a total radial shaft seal failure.

[0013] The invention solves this problem through the subject matter of claim 1.

[0014] This advantageous design and the method according to claim 3 open up a wide variety of options.

[0015] This design enables pressure measurement within the respective chamber in a structurally simple and therefore advantageous manner. The pressure gauge allows the gas pressure Pact in the chamber and / or in a space adjacent to the chamber to be determined. The pressure gauge can be operatively connected to the control and / or regulating device.

[0016] In this way, it becomes possible to reduce the wear of the radial shaft seals in a simple way, since it is possible to easily detach them from the shaft during operation, where their free ends would otherwise be in contact, to such an extent that the friction and the associated wear in this area are reduced.

[0017] Since a gas source is connected to the pipe, a structurally simple method is created to pressurize the respective chamber (if applicable). This design can then be used to advantageously determine the current wear level of the seals, as well as to estimate or predict a total seal failure, thus enabling predictive maintenance of the seals.

[0018] And since one of the sealing arrangements is positioned on each side of the bearing to be protected, and since the respective sealing lips of the radial shaft seals of the respective chamber are directed away from the respective chamber in opposite directions, the bearing is thus protected axially on both sides by one of the advantageous sealing arrangements.

[0019] It is advantageous and simple if each chamber can be pressurized with gas pressure via a bore and / or a pipe.

[0020] Furthermore, it can be advantageously and structurally simple to provide that an orifice is arranged or formed between the gas source and the sealing arrangements of the respective chamber.

[0021] The problem is also solved by the method according to claim 3.

[0022] According to claim 3, a method for operating a solid-bowl screw centrifuge is provided, in which an incoming suspension Su is separated into at least one liquid phase FI and at least one solid phase Fe, wherein during the separation, a gas pressure Pact is generated in the respective chamber of the at least one sealing arrangement with two radial shaft seals by a gas source operatively connected to the respective chamber, wherein the gas pressure Pact is increased at least up to a gas pressure Pmax at which the radial contact of the respective sealing lip is overcome, so that gas leakage at the sealing lips of the respective radial shaft seal begins at a leakage pressure Pmax. The current leakage pressure Pact, which corresponds to the current gas pressure Pact in the chamber, is measured and the currently measured leakage pressure Pact is compared with at least one stored reference value.The current wear condition of the respective sealing lip or sealing arrangement is then determined and / or evaluated by comparing the currently measured leakage pressure P akt with at least one stored reference value.

[0023] According to claim 4, a further development of claim 3 provides a method for operating a solid-wall screw centrifuge, in which an incoming suspension Su is separated into at least one liquid phase FI and at least one solid phase Fe, wherein during the separation a gas pressure Pact is generated in the respective chamber of the at least one sealing arrangement with two radial shaft seals by a gas source operatively connected to the respective chamber, wherein the respective chamber is pressurized with the gas pressure by a respective orifice and / or such that the feed volume is limited by the respective orifice and wherein the feed pressure Pzu upstream of the respective orifice is at least temporarily set such that the radial contact of the respective sealing lip is overcome by the gas pressure Pact in the chamber, so that a gas leakage at the sealing lips of the respective radial shaft seal begins at a leakage pressure Pmax.The current leakage pressure Pact, which corresponds to the current gas pressure Pact in the chamber, is measured and compared with at least one stored reference value. The current wear condition of the respective sealing lip or sealing assembly is then determined and / or evaluated based on this comparison.

[0024] In this way, the wear of the respective sealing rings can be advantageously reduced or decreased during operation.

[0025] The gas pressure can be advantageously adjusted individually according to the requirements of the respective radial shaft seals installed and the size of the respective centrifuge.

[0026] The gas pressure Pzu is increased – for example, by the control and / or regulating device and the gas source – for a new set of seals up to a gas pressure Pmax at which gas leakage begins at a sealing lip of the respective radial shaft seal. This creates a simple reference value for the maximum pressure and then also for the leakage pressure Pmax.

[0027] The maximum leakage pressure Pmax is stored as a reference value – particularly in the control and / or regulating device. This allows the reference value to be conveniently retrieved at any time for comparison purposes.

[0028] The current leakage pressure P max is measured in each case. This allows for a simple and therefore advantageous representation of the current condition of the seal.

[0029] Since the currently measured leakage pressure P max is compared with at least one stored reference value for the leakage pressure P max, a conclusion can be drawn about the current wear state of the seal in a simple and therefore advantageous way.

[0030] The current wear condition of the respective sealing lip is determined and / or evaluated. This is done by comparing the current leakage pressure with one or more stored reference values, allowing the remaining service life of the seal to be specified. This advantageously enables predictive maintenance of the seal.

[0031] According to claim 3, the orifice in the respective gas line is initially dimensioned such that a defined small quantity of gas can escape through the respective sealing lips. This is because the quantity of gas supplied per unit of time to the respective chamber can be limited by the orifice at a constant supply pressure P > Pmax. A leakage gas flow occurs when the supply pressure is greater than the leakage pressure Pmax, whereby a relatively constant gas flow can result depending on the orifice opening. The leakage gas flow thus establishes itself behind the orifice or in the chamber, and this flow can, in turn, depend on the wear condition of the sealing lips. The measured value of this gas pressure can be compared in a control system with stored reference values ​​for the leakage pressure. This allows conclusions to be drawn about the wear condition of the seal or the sealing assembly.A gas pressure regulating device and a flow measurement are not required, so this method can be designed to be particularly simple.

[0032] Further advantageous embodiments of the invention can be found in the dependent claims.

[0033] The invention is described in more detail below with reference to the drawing and exemplary embodiments. The invention is not limited to these exemplary embodiments, but can also be implemented differently within the scope of the claims. Furthermore, individual features of the following exemplary embodiments can also be combined with other exemplary embodiments. The drawings show: Figure 1: a schematic, sectional view of a solid-bowl screw centrifuge; Figure 2: a section of a drum shaft bearing of a solid-bowl screw centrifuge, in particular of the type of Fig. 1Figure 3: a diagram showing the friction loss versus the circumferential speed of a radial shaft seal of the solid-wall screw centrifuge Fig. 1 Figure 4 shows a measurement record of a first test with a pair of radial shaft seals on a first bearing "FLT" and a second bearing "FS". Figure 5 shows a measurement record of a second test with a pair of radial shaft seals on a first bearing "FLT" and a second bearing "FS".

[0034] The terms "right", "left", "horizontal", "vertical" used below refer to the respective drawing plane.

[0035] Fig. 1 Figure 1 shows a solid-jacket screw centrifuge with a frame that is not rotatable or rotating during operation and preferably a housing 100 and a rotor 200 that is rotatable or rotating during operation.

[0036] The rotor 200 has a rotatable drum 210 with a horizontal axis of rotation D. However, the axis of rotation D can also be oriented differently in space, particularly vertically. The rotor 200 also includes a screw 230 arranged inside the drum 210, the axis of rotation of which coincides with that of the drum 210. During operation, the screw 230 can be rotated at a differential speed with respect to the drum 210.

[0037] The drum 210 has a cylindrical section 211 on the inside and outside and a conical section 212 adjoining it axially on the inside and outside. The cylindrical section 211 is closed off by a drum cover 213 extending substantially radially.

[0038] The screw 230 also has a section 231 that is at least cylindrical on the outside and a section 232 that is at least conical on the outside and axially adjoining it. It is arranged inside the drum 210. The drum 201 is rotatable during operation. The screw 230 is also rotatable during operation. Preferably, the two elements, drum 210 and screw 230, are rotated relative to each other at a differential speed during operation. One or more suitable drives, e.g., electric motors, are used for this rotation.

[0039] Into the drum 210 protrudes an inlet pipe 214, which runs concentrically to the axis of rotation and leads into a distributor 215, through which a suspension Su to be processed can be directed radially into a centrifugation chamber 216 of the drum 210.

[0040] The inlet pipe 214 can either be led into the drum 210 from the side of the cylindrical drum section 211 or it can be led into the drum 210 from the side of the conical drum section 212.

[0041] One or more liquid outlets 217 can be formed in or on the drum lid 213. These can be designed in various ways, such as openings in the drum lid 213 that have a type of overflow weir, or in other ways, such as a skimming disc. At least one solids discharge 218 is formed in the area of, and in particular at the end of, the conical section 212.

[0042] The drum 210 is typically designed as a solid drum. Inside the rotating drum 210, the suspension is clarified, or at least separated into a liquid phase (FI) and a solid phase (Fe). The liquid phase (FI) exits through the liquid outlet 217 at the drum lid 213. The solid phase (Fe) is transported by the screw conveyor 230 towards the solids discharge 218 and ejected from the drum 210 there.

[0043] A first drum shaft section 220 is axially connected to the drum cover 213 or to the actual drum 210 and is rotationally fixed to the drum 210. A second drum shaft section 219 is axially connected to the conical drum section 212 and is also rotationally fixed to the drum 210.

[0044] A first screw shaft section 234 is axially connected to the cylindrical section 231 of the screw 230 and is rotationally fixed to the screw 230, and a second screw shaft section 233 is axially connected to the conical drum section 232 and is also rotationally fixed to the screw 230.

[0045] Here, the axis of rotation D is horizontally oriented. The axis of rotation can also be vertically or diagonally oriented (not shown here). The drum and / or the screw can also be supported on one side only.

[0046] A drive device 300 with one or two motors (not shown here) serves to drive the rotor 200. At least one gearbox 310 can be connected downstream of the drive device 300. Two pulleys 320 and 330 are shown schematically as examples of this gearbox, indicating that the gearbox 310 can have at least two interfaces for feeding a respective torque from the electric motor(s) into the gearbox 310 to drive the drum and the worm gear.

[0047] Alternatively (not shown here), the rotor can be driven differently, for example by hydraulic motors, so that a gearbox may not be necessary. The drive can also be achieved by a combination of electric motor(s) and hydraulic motor(s), in which case different gearboxes are used and the pulleys are either completely or partially omitted.

[0048] The drive thus rotates both the drum 210 and the worm 230. For this purpose, the gearbox 310 has two output shafts. The first output shaft is rotationally fixed to the first drum shaft section 220 or directly coupled to the drum 210, and the second output shaft is directly or indirectly rotationally fixed to the first worm shaft section 234 or directly to the worm 230.

[0049] The drum 210 and the shaft are each rotatably mounted by two drum bearings 221, 222 arranged axially in the direction of the axis of rotation. The term "bearing" should therefore not be interpreted too narrowly. Each of the bearings 221, 222 can consist of one or more individual bearings, which are then arranged axially directly adjacent to one another, so that they can each be considered functionally as a single bearing. The bearings 221, 222 can also be designed as bearings of various types, such as rolling bearings – in particular ceramic bearings, hybrid ceramic bearings, magnetic bearings, or plain bearings.

[0050] The drum bearings 221, 222 are arranged between the drum 210 and the frame 100 or a part connected to the frame, so that the drum 210 can be rotated relative to the frame 100. The drum bearings 221, 222 are preferably arranged radially between the drum 210 and the frame 100 or a part connected to the frame.

[0051] The screw bearings 235, 236, on the other hand, are arranged radially between the screw 230 and the drum 210, so that the screw 230 is rotatable relative to the drum 210. The screw bearings 235, 236 are preferably arranged radially between the drum 210 and the screw 230.

[0052] In one possible embodiment (not shown), one of the screw bearings 235 in the area of ​​the solids discharge 218 can be omitted. In this case, the rotating screw centers itself, which is known, for example, in a vertical arrangement of the decanter.

[0053] Axially to the left and right of one of the bearings, in particular the drum bearings – here, for example, next to the drum bearing 221 on the conical drum section 212 – at least one sealing arrangement – ​​here two sealing arrangements – is arranged. These are intended to seal the respective bearing to which they are assigned during the processing of the suspension, in particular against the ingress of suspension or suspension components. The bearing to be protected can be axially protected by one of the sealing arrangements or be arranged between two sealing arrangements. Alternatively, it can also be axially protected on only one side by a single sealing arrangement (not shown here).

[0054] Each sealing arrangement comprises two radial shaft seals 400a, b, or 400c, d, respectively, arranged at an axial distance from each other, forming a chamber 402a, b between the two radial shaft seals 400a, b. Radially inward, the respective chamber 402a is bounded by the shaft 219 or a portion thereof. Radially outward, it may additionally be bounded by the ring or sleeve section 110.

[0055] One of the two sealing arrangements seals the drum bearing 221 axially against a collection chamber 101 for the solid phase Fe, and the other sealing arrangement seals it axially to the other side – for example, against the environment. In this respect, the respective sealing arrangement 400 protects the drum bearing 221, 222 against the ingress of components of the suspension Su from the corresponding axial side.

[0056] A radial shaft seal 400 within the meaning of this document is a seal which is used to seal rotating elements, such as rotating shafts, in particular those which are rotatably mounted in a ring or sleeve section 110 of the housing 100.

[0057] The respective radial shaft seals 400 have a sealing lip 401 that rests on the surface of the rotating shaft. The sealing lip 401 is designed to press radially against the shaft surface or a shaft sleeve 405, thus generating a sealing force that acts on the shaft or the shaft sleeve 405 and creates a seal. A coil spring or worm spring may also be provided for this purpose. The radial shaft seals may have a reinforcing ring, e.g., made of metal. They are fixed externally in the ring or sleeve section 110.

[0058] The aforementioned storage site is located in Fig. 2Shown enlarged. The four radial shaft seals 400a, b, c, d are arranged in pairs axially to the left and right of the drum bearing 221, thus forming two of the sealing arrangements.

[0059] The radial shaft rings 400a, b, c, d can in particular be fixed (radially outwards) to a surrounding ring or sleeve section 110, which can be an element of, for example, the frame or housing.

[0060] The sealing lips 401 of each pair of radial shaft seals 400a, b and 400c, d respectively contact a respective shaft sleeve 405, which is mounted on the drum shaft section 219. The shaft sleeve 405 forms the running surface or counter-sealing surface of the paired radial shaft seals 400a, b, c, d. The paired radial shaft seals 400a, b and 400c, d are oriented such that the sealing lips 401 of each pair point outwards, i.e., away from the respective chamber 402a, b.

[0061] The respective chamber 402a, b is laterally bounded by the sealing lips 401 of the two radial shaft seals 400a, b and 400c, d, respectively, and radially inwardly by the drum shaft section 219 and / or the respective shaft sleeve 405. Radially outwardly, it may also be bounded by the ring section 110. A gas supply line opens into the chamber. This gas can be supplied from a gas source 600. The gas source can be a compressed air tank and / or a compressor.

[0062] It is advantageously provided that the respective sealing lips 401 of the radial shaft seals 400a, b and 400c, d of the respective chambers 402a, b are directed away from the respective chambers 402a, b in opposite directions, so that the two sealing lips 401 can each be lifted radially outwards by a gas pressure in the chamber. The sealing lips 401 describe a kind of arc that transitions from the radial direction to an axial direction, whereby the axial section can bear against the rotating element on the inside. The axial ends or sections of the two sealing lips 401 on one of the chambers 402a, b are thus directed outwards away from each other. If they were directed inwards towards each other, they could not be lifted by a gas pressure in the chamber 402a, b, but would instead be pressed even more firmly against the rotating element with increasing gas pressure.

[0063] The gas source 600 can, for example, have a valve downstream that can be controlled by the control and / or regulating unit 500. The compressor 600 can also be controlled by the control and / or regulating unit 500 (schematically shown in [reference]). Fig. 2 (hinted at but not shown in detail).

[0064] A bore 403a, b opens into the respective chamber 402a, b in the ring or sleeve section 110, to which a line 404a, b can be connected, leading to the gas source 600. Via the line 404a, b and the bore 403a, b, the respective chamber 402a, b can be pressurized with a gas pressure P from the gas source 600, for example, a compressed air source, resulting in a current gas pressure Pact in the chamber 402a, b.

[0065] It may include a pressure gauge or pressure sensor with which the gas pressure Pact in the respective chamber 402a, b can be measured or sensed. This may, for example, be provided in the respective line 404a, b. The gas for generating the gas pressure is supplied by means of the gas source 600. This may be designed to be controllable.

[0066] As in Fig. 3 As can be seen, the contact pressure of the sealing lip 401 is a parameter for the amount of friction losses. If the respective chamber 402a, b is now pressurized with a gas pressure Pact, the sealing lip 401 is lifted by the gas pressure Pact due to its shape and arrangement (sealing lip points outwards). Thus, the gas pressure Pact counteracts the contact pressure of the respective sealing lip 401 and therefore reduces the contact pressure of the sealing lip 401 on the shaft sleeve 405 or the drum shaft section 219, thereby reducing the friction losses.

[0067] In a pair of radial shaft seals 400a, b and 400c, d, each with an intact sealing lip 401, the sealing lip 401 lifts off from the shaft sleeve 402 or the drum shaft section 219 in the respective chamber 402a, b at a certain gas pressure Pact = Pmax. This results in a corresponding gas leakage.

[0068] With the aid of a suitable control and / or regulating device, which, for example, controls a valve downstream of the gas pressure source or a compressor (not shown here), the gas pressure Pact can be changed. The gas pressure Pact in the respective chamber 402a, b can thus be increased with a new sealing lip 401 up to a gas pressure Pmax at which a leak begins.

[0069] As the sealing lip 401 wears down, the measured value for the gas pressure Pmax, at which leakage begins, becomes progressively smaller and can be compared in the control and / or regulating unit 500 (which is, in particular, a computer with interfaces and a memory) with reference values ​​for the gas pressure Pmax, at which leakage should begin. This allows conclusions to be drawn about the wear condition of the respective sealing lip 401. In addition to pressure measurement, this procedure also requires pressure control and flow measurement.

[0070] Alternatively, the amount of gas supplied per time to the respective chamber 402a, b can be limited by an orifice 406a, b at a constant supply pressure Pto > Pmax. This results in a leakage gas flow, since the supply pressure Pto is greater than the leakage pressure Pmax, so that a relatively constant gas flow is generated depending on the orifice opening, which overcomes the respective sealing lip 401.

[0071] Behind the orifice, or in the respective chamber 402a, b, a current gas pressure or leakage pressure Pact is established, which depends on the wear condition of the respective sealing lip 401. The measured value of this gas pressure in the respective chamber 402a, b can be compared with reference values ​​in a control system and provides information about the wear condition of the respective sealing lip 401. A pressure control device and a flow measurement are not required for this purpose.

[0072] Fig. 4Figure 1 shows a measurement record from a test on a solid-wall screw centrifuge. The seal diameter in this test is 110 mm, and the solid-wall screw centrifuge is operated at a speed of 6500 rpm. In this test with a pair of radial shaft seals 400a, b and 400c, d on a first bearing "FLT," the gas pressure Pact in chamber 402a, b between the radial shaft seal pair was reduced from 150 mbar to 8 mbar. The gas leakage decreased from 980 NI / h to 0 NI / h, while the bearing temperature increased from 100°C to 122°C.

[0073] Fig. 4Figure 1 shows a further measurement record from another test with a pair of radial shaft seals 400a, b and 400c, d on a second bearing "FS", in which the gas pressure Pact in chamber 402a, b between the radial shaft seal pair was reduced from 145 mbar to 4 mbar. The gas leakage decreased from 3000 NI / h to 0 NI / h, while the bearing temperature increased from 58°C to 70°C.

[0074] The relationship between increased frictional power of the respective sealing lip 401 and reduced gas pressure P akt in the chamber 402 a, b is clearly evident here.

[0075] Fig. 5Figure 1 shows a measurement record from another test on a solid-bowl screw centrifuge. In this test, the seal diameter is 110 mm, and the solid-bowl screw centrifuge is operated at a speed of 6500 rpm. In this test, with a pair of radial shaft seals 400a, b and 400c, d on the first bearing "FLT," the gas pressure Pact in chamber 402a, b between the radial shaft seal pair was increased from 50 mbar to 100 mbar. No gas leakage occurred, and the bearing temperature decreased from 122.5°C to 115°C.

[0076] Fig. 5 Figure 1 shows a further measurement record from another test with a pair of radial shaft seals 400a, b and 400c, d on a second bearing "FS", in which the gas pressure in chamber 402a, b between the radial shaft seal pair was increased from 50 mbar to 100 mbar. The gas leakage increased from 980 NI / h to 1700 NI / h while the bearing temperature decreased from 69°C to 61°C.

[0077] The relationship between the reduced frictional power of the respective sealing lip 401 at increased gas pressure P akt in chamber 402 a, b is also clearly visible here.

[0078] For the operation of a solid-jacket screw centrifuge, in which an incoming suspension Su is separated in the rotating drum 210 into a solid phase Fe and at least one liquid phase FI, the following method is preferably specified: The gas pressure P akt in the respective chamber 401a, b of the respective sealing arrangement with two radial shaft seals 400a, b, c, d can be set by the control and / or regulating device and by one or more components controllable by this control and / or regulating device, in particular valves and / or a compressor or the like as a pressure source.

[0079] In this way, the respective chamber is subjected to a gas pressure P ZU, which results in a gas pressure P akt in the chamber.

[0080] The gas pressure P akt can be increased by the control and / or regulating device up to a gas pressure P max at which a gas leakage begins at a new sealing lip 401 of the respective radial shaft seal 400a, b, c, d, as this lifts off from the shaft.

[0081] In this way, the wear on the sealing lip(s) of the respective radial shaft seals 400a, b, c, d can be reduced.

[0082] In practice, for example, the supply pressure PZU and the orifice cross-section can be selected to achieve a defined flow rate, such as a flow rate of a few hundred to several thousand N / h, for example approximately 400 N / h (N / h: standard volumetric flow rate / h) per pair of radial shaft seals (i.e., per chamber). This is documented in the measurement protocol of the Fig. 4An example with 3000 NI / h (with pressure control) is included. The amount of the leakage pressure P max corresponding to the defined flow rate of a new sealing arrangement 400 can be stored as a reference value - e.g. in the control and / or regulating device 500.

[0083] Then, or during this process, the current leakage pressure Pact in or at the respective chamber can be measured using a measuring device (not shown). This can be done continuously or at defined time intervals.

[0084] The currently measured leakage pressure Pact is then compared with one or more stored reference values. This can be done continuously or at defined time intervals.

[0085] The current wear condition of the respective sealing arrangement 400 can then optionally be assessed. This can be done easily, for example, using at least one table of values ​​stored in the control and / or regulation unit 500, in which corresponding pairs of values ​​for the respective leakage pressure Pact and the associated degree of wear are stored.

[0086] A message is generated when the current wear condition exceeds a defined threshold, so that the respective radial shaft seal 400a, b, c, d must be replaced.

[0087] This variant thus provides a simple way to measure the current wear level of the sealing lip 401, as well as to estimate or predict a total failure of a radial shaft seal 400a, b, c, d, so that predictive maintenance of the radial shaft seals 400a, b, c, d is possible. List of designations

[0088] 100 Housing 101 Collection chamber 110 Ring or sleeve section 200 Rotor 210 Drum 211 Cylindrical section 212 Conical section 213 Drum cover 214 Inlet pipe 215 Distributor 216 Centrifugal chamber 217 Liquid outlet 218 Solids discharge 219 Drum shaft section 220 Drum shaft section 221 Drum bearing 222 Drum bearing 230 Worm 231 Cylindrical section 232 Conical section 233 Worm shaft section 234 Worm shaft section 235 Worm bearing 236 Worm bearing 300 Drive device 310 Gearbox 320 Pulley 330 Pulley 400 Sealing arrangement 400a, b, c, d Radial shaft seal 401 Sealing lip 402a, b Chamber 403a, b Bore 404a, b Line 405 Shaft sleeve 406a, b Cover 500 Control and / or regulating device 600 Gas source D-axis rotation SuSuspension Fe solids FI liquid phase P to feed pressure P max maximum pressure P akt akt gas pressure, leakage pressure

Claims

1. Solid bowl screw centrifuge for separating an inflowing suspension into at least one liquid phase Fl and at least one solid phase Fe, comprising at least: a. a rotatable drum (210) having an axis of rotation (D), wherein the drum (210) has a cylindrical portion (211) and a conical portion (212), b. at least one feed for a suspension (Su), at least one liquid drain (217), and at least one solid discharge (218), c. a screw (230) arranged in the drum and rotatable relative to the rotatable drum (210) with a differential speed, d. at least one or more drum bearings (221,222) for bearing the drum (210) in a housing (100), e. at least one or more screw bearings (236) for bearing the screw (230) in the drum (210), f. at least one sealing assembly (400) arranged between a drum shaft portion (219, 220) and the housing (100) for protecting at least one of the bearings, in particular at least one of the drum bearings (221, 222), against ingress of constituents of the suspension Su, g. wherein the respective sealing assembly (400) comprises at least two radial shaft sealing rings (400a, b, c, d) which are arranged at a mutual axial spacing to form at least one respective chamber (402a, b), h. wherein a gas pressure can be applied to the respective chamber (402a, b) by means of a gas source (600), so that a current gas pressure Pakt is established therein, i. wherein the chamber (402a, b) can be pressurized with the gas pressure by means of a control and / or regulating device and the gas source (600), wherein the gas pressure Pakt in the respective chamber (402a, b) can be varied by means of the control and / or regulating device (500), and j. wherein the respective line (404a, b) has a pressure measuring device and / or a pressure sensor with which the current gas pressure Pakt in or outside the respective chamber (402a, b) can be measured or sensed, characterized in that k. the respective radial shaft sealing rings (400a, b, c, d) are arranged such that their respective sealing lips (401) are directed away from the respective chamber (402a, b), l. the respective chamber (402a, b) can each be pressurized with the gas pressure via a bore (403a, 403b) and / or a line (404a, b), and m. the respective bore (403a, b) and / or the respective line (404a, b) comprises or forms an orifice plate (406a, 406b).

2. Solid bowl screw centrifuge according to claim 1, characterized in that one of the sealing assemblies (400) is arranged on each side of the respective bearing to be protected and in that the respective radial shaft sealing rings (400a, b, c, d) of the respective chamber (402a, b) are in each case directed away from the respective chamber (402a, b) in opposite directions.

3. Method for operating a solid-bowl centrifugal separator for separating an inflowing suspension into at least one liquid phase (FI) and at least one solid phase (Fe), comprising at least: - a rotatable drum (210) having an axis of rotation (D), wherein the drum (210) has a cylindrical portion (211) and a conical portion (212), - at least one feed for a suspension (Su), at least one liquid drain (217), and at least one solid discharge (218), - a screw (230) arranged in the drum and rotatable relative to the rotatable drum (210) with a differential speed, - at least one or more drum bearings (221,222) for bearing the drum (210) in a housing (100), - at least one or more screw bearings (236) for bearing the screw (230) in the drum (210), - at least one sealing assembly (400) arranged between a drum shaft portion (219, 220) and the housing (100) for protecting at least one of the bearings, in particular at least one of the drum bearings (221, 222), against ingress of constituents of the suspension Su, - wherein the respective sealing assembly (400) comprises at least two radial shaft sealing rings (400a, b, c, d) which are arranged at a mutual axial spacing to form at least one respective chamber (402a, b), - wherein a gas pressure can be applied to the respective chamber (402a, b) by means of a gas source (600), so that a current gas pressure Pakt is established therein, - the respective radial shaft sealing rings (400a, b, c, d) are arranged such that their respective sealing lips (401) are directed away from the respective chamber (402a, b), - wherein the chamber (402a, b) can be pressurized with the gas pressure by means of a control and / or regulating device and the gas source (600), wherein the gas pressure Pakt in the respective chamber (402a, b) can be varied by means of the control and / or regulating device (500), and - wherein the respective line (404a, b) has a pressure measuring device and / or a pressure sensor with which the current gas pressure Pakt in or outside the respective chamber (402a, b) can be measured or sensed, in which method an inflowing suspension Su is separated by the solid bowl screw centrifuge into at least one liquid phase Fl and at least one solid phase Fe, characterized in that during the separation in the respective chamber (402a, b) of the at least one sealing assembly (400) with in each case two radial shaft sealing rings (400a, b, c, d), by means of a gas source (600) a gas pressure Pakt is generated by a gas source operatively connected to the respective chamber (402a, b), wherein the current gas pressure Pakt is increased at least up to a gas pressure Pmax at which the radial contact of the respective sealing lip (401) is overcome, so that a gas leakage at the sealing lips (401) of the respective radial shaft sealing ring (400a, b, c, d) starts at a leakage pressure Pmax, in that the current leakage pressure Pakt, which corresponds to the current gas pressure Pakt in the chamber, is measured, and in that the currently measured leakage pressure Pakt is compared with at least one stored reference value, and in that the current state of wear of the respective sealing lip (401) or of the sealing assembly (400) is determined and / or evaluated on the basis of the comparison of the currently measured leakage pressure Pakt with the at least one stored reference value.

4. Method according to claim 3, in which method an inflowing suspension Su is separated by the solid bowl centrifuge into at least one liquid phase Fl and at least one solids phase Fe, characterized in that during the separation in the respective chamber (402a, b) of the at least one sealing assembly (400) with in each case two radial shaft sealing rings (400a, b, c, d), a gas pressure Pakt is generated by a gas source (600) operatively connected to the respective chamber (402a, b), wherein the respective chamber is acted upon by the gas pressure through the respective orifice plate (606a, b) and the feed volume is limited by the respective orifice plate (406a, b), and wherein the feed pressure Pzu upstream of the respective orifice plate (406a, b) is set in such a way that the radial contact of the respective sealing lip (401) is overcome by the gas pressure Pakt in the chamber, so that a gas leakage at the sealing lips (401) of the respective radial shaft sealing ring (400a, b, c, d) begins at a leakage pressure Pmax, wherein the current leakage pressure Pakt, which corresponds to the current gas pressure Pakt in the chamber, is measured, and in that the currently measured leakage pressure Pakt is compared with at least one stored reference value, and in that the current state of wear of the respective sealing lip (401) and / or of the sealing assembly (400) is determined and / or evaluated on the basis of the comparison of the currently measured leakage pressure Pakt with the at least one stored reference value.

5. Method according to one of claims 3 or 4, characterized in that a message is generated and preferably output if the current state of wear exceeds a defined threshold value, so that the respective radial shaft sealing ring (400a, b, c, d) must be replaced.